The invention concerns an actuating cylinder according to the definition of the species of Patent claim 1 and a method for assembling same according to Patent claim 12. In particular, the invention concerns an actuating cylinder for a hydraulic clutch operation device in a motor vehicle such as those mass produced in the industry.
German Patent Publication DE 3,816,608 A1 discloses an actuating cylinder having a housing in which there is a piston that is guided by a guide part and can be displaced by means of a piston rod. This actuating cylinder serves as a master cylinder in a hydraulic clutch operation device, which is connected by the piston rod to the clutch pedal of the motor vehicle and is connected by a pressure line to a slave cylinder, so that the pressure generated in the pressure chamber of the actuating cylinder due to the displacement of the piston when the clutch pedal is depressed can be transmitted to the slave cylinder through the liquid column in the pressure line. As a result, the release bearing of the clutch of the motor vehicle is acted on by the slave cylinder with an actuating force to separate the clutch thrust plate from the clutch driving plate by a release mechanism and thus separate the combustion engine from the transmission of the motor vehicle.
With this state of the art, the end of the piston on the pressure chamber side of the actuating cylinder that forms a receptacle for the piston rod on the side facing away from the pressure chamber is made of plastic. In operation of the actuating cylinder, it is essential to prevent the piston from striking the bottom of the housing of the actuating cylinder when the clutch pedal is depressed, because the excess actuating forces, also referred to as forces of improper use, could result in an excessive pressure burden between the piston and the housing bottom on the one hand and the piston and piston rod on the other hand, which could lead to damage to the piston. To prevent this, the end of the piston rod on the pedal side is provided with a thread onto which a nut is screwed as a lock nut when the actuating cylinder is installed in the motor vehicle, wherein the lock nut works together with a stationary control element to limit the working stroke of the piston.
Although with this prior art, smooth guidance of the piston in the housing of the actuating cylinder is assured by the guide part, it is a disadvantage here that adjusting the working stroke of the piston requires additional steps when the actuating cylinder is installed in the motor vehicle, and this can be relatively expensive due to the scattering in manufacturing tolerances on the actuating cylinder and the clutch pedal or pedal block.
The same problem is also encountered with the actuating cylinder known from German Patent Publication DE 3,816,610 A1, which differs from the prior art according to German Patent Publication DE 3,816,608 A1 in that the guide part is detachably attached to the housing of the actuating cylinder by means of a threaded section.
Furthermore, German Patent Publication DE 3,149,628 A1 discloses an actuating cylinder whose piston is provided with a central valve on the end on the side of the pressure chamber. This piston also must not strike the bottom of the housing of the actuating cylinder because that could cause damage to the central valve. According to this state of the art, the end of the piston rod on the pedal side is provided with a piston rod head having a fastening eye by means of which the piston rod is operatively connected to the clutch pedal. The working stroke of the piston is limited here between the clutch pedal and the pedal block, both of which must have a narrow tolerance when the actuating cylinder is completely preassembled, which is associated with a high manufacturing cost accordingly.
In addition, it is also known, e.g., from German Patent Publication DE 3,738,512 A1 that the piston of a slave cylinder can be designed so it can strike the housing bottom of the slave cylinder without being damaged. However, with this state of the art there are problems in that the piston must be made of suitably strong materials, which are thus also expensive, and/or the pistons must be made of larger dimensions accordingly to have adequate strength in view of the forces of improper use that can be expected.
Finally, German Patent Publication DE 3,525,029 A1 discloses a piston-cylinder arrangement where the stroke is limited by a stop mechanism consisting of a fixed stop mounted on the outside of the cylinder and a counterstop that works together with it. The counterstop consists of a threaded section provided on the piston rod on which is screwed a threaded ring that is detachably secured in the axial direction of the piston rod by means of a retention device in the form of a counternut or a locking screw that sits in a threaded bore introduced radially into the threaded ring. This prior art suffers from the disadvantage that the design of the counterstop and its assembly on the piston rod are relatively expensive.